A computer system normally includes a video display terminal which usually provides user feedback with a cursor to enable the user to either select an elemental area of the screen in the case of a mouse, or an elemental area of the digitizing surface in the case of a digitizer. There have previously been proposed various types of cursor control systems such as light pens, mice, track balls and other devices which require the use of a wire to either communicate positional information or carry electrical signals for measurement of position by various means.
A light pen includes a stylus with a photoelectric detector which is held to a CRT to detect the time when an electron beam passes its position. It must be used with a scanning CRT, it operates on light emitted by the CRT, and it is different from all acoustic digitizers. See, for example, U.S. Pat. No. 3,825,746.
A track ball is a ball which can be rotated in any direction within a fixed socket. A computer senses the direction and extent of movement, usually by means of wheels which rub against the ball in orthagonal directions. Each wheel is connected to a tachometer which indicates movement and direction of each such wheel. This is a relative device which cannot provide absolute position information. Further, this device requires a mechanical connection between the positioning element and the measuring system.
A touch pad involves the use of a flat pad which can be touched by a stylus or a finger. The pad senses the location of the touching object usually by resistance or capacitance disturbances in the field associated with the pad. A touch pad can also use acoustic surface waves, e.g., see U.S. Pat. No. 3,653,031.
Mechanical mice have also been used previously. See, for example, U.S. Pat. No. 4,464,652. Basically such devices involve an upside down track ball which is rolled across the desk or other work surface by the operator. Such devices require a wire connection to the computer and there must be frictional contact with the surface. Because these are mechanical systems there are also inherent mechanical problems with such systems. Good frictional contact must be maintained with the work surface. The mice also include a number of components which must be made with close tolerances. The mice may also generate mechanical noise and must be frequently cleaned.
Optical mice are also described in U.S. Pat. Nos. 4,364,035 and 4,390,873. These devices reflect light off of a pattern on a pad. As the pattern of the reflected light changes, the mouse can determine the direction and velocity of movement of the device. Thus, such devices require the use of a special pad over which the mouse operates. Such devices also require use of a wire connection to the computer.
There has also been proposed a mouse which utilizes cloth to generate acoustic energy which it then measures in order to determine the speed at which the mouse is moving but cannot determine direction by acoustic means. The cloth rubs upon the work surface to generate the sound. The system requires use of a wire connection, and it does not generate an acoustic wave.
The mice which have previously been used are relative devices which only report movement, as opposed to digitizers which report absolute position.
There have also been proposed magnetic and electrostatic digitizers which involve the use of a pad over which a stylus or puck may operate. The stylus or puck generates an electromagnetic or electrostatic signal and the pad receives it. In some devices, however, the stylus may receive and the pad may transmit. The pad contains horizontal and vertical rows of wires and can interpolate the position of the stylus or puck between any two wires. The devices operate on signal amplitude and phase and are subject to electromagnetic and electrostatic interference. Electrostatic digitizers operate poorly on conductive surfaces. See U.S. Pat. No. 3,904,822.
There have also been proposed spark digitizers which generate an acoustic wave, usually from a spark transmitter. See, e.g., U.S. Pat. Nos. 4,012,588; 4,357,672; and 3,838,212. The position of the stylus is determined by timing the transit time of the acoustic wave from the source to the receiver. There are several disadvantages with such spark digitizers. The spark is a shock hazard and may also be a fire hazard. The spark also generates electromagnetic interference and makes audible noise. It is also necessary for the spark to be synchronized with the receiver timers. Of course, such digitizers also require use of a wire to carry the necessary power to generate the spark and to carry switch information. Although wireless spark digitizers are also described in U.S. Pat. Nos. 4,012,588 and 4,124,838, they exhibit most of the same disadvantages described above with respect to spark digitizers using a wire. They also provide no capability for incorporating switches into the wireless device nor are they adaptable to a stylus type steering means.
Systems which require a wire connection between the movable device and the computer have several inherent disadvantages. For example, the wire is cumbersome and expensive to produce in a flexible form. Also, it can be kinked and twisted. Accordingly, it can be broken or operate intermittently. Systems which require active pads on which the movable device operates are quite expensive, and the large pad is difficult to store when not in use. There are also significant power requirements inherent with such systems.